Methanosarcina acetivorans
Encyclopedia
Methanosarcina acetivorans is a versatile methane producing microbe
which is found in such diverse environments as oil wells, trash dumps, deep-sea hydrothermal vents, and oxygen-depleted sediments beneath kelp beds. Only M. acetivorans and microbes in the genus Methanosarcina
use all three known metabolic pathways for methanogenesis
. http://www.genome.org/cgi/reprint/12/4/532.pdf Methanosarcinides, including M. acetivorans, are also the only archaea
capable of forming multicellular colonies, and even show cellular differentiation. , the genome of M. acetivorans is the largest of all sequenced archaeal genomes.
In 2006, James G. Ferry and Christopher House discovered that M. acetivorans uses a previously unknown metabolic pathway
to metabolize carbon monoxide
into methane
and acetate
using the well known enzymes phosphotransacetylase (PTS) and acetate kinase
(ACK). This pathway is surprisingly simple, and has been proposed by Ferry and House as perhaps the first metabolic pathway used by primordial microbes. Other theories of the primordial metabolic biochemistry include heterotrophic theory and chemoautotrophic theory, but both these theories have been criticised as being far too complex to have arisen spontaneously.
However, in the presence of minerals containing iron sulfides, as might have been found in sediments in a primordial environment, acetate would be catalytically converted into acetate thioester, a sulfur-containing derivative. Primitive microbes could obtain biochemical energy in the form of adenosine triphosphate
(ATP) by converting acetate thioester back into acetate using PTS and ACK, which would then be converted back into acetate thioester to complete the process. In such an environment, a primitive "protocell" could easily produce energy through this metabolic pathway, excreting acetate as waste. Furthermore, ACK catalyzes the synthesis of ATP directly. Other pathways generate energy from ATP only through complex multi-enzyme reactions involving protein pumps and osmotic imbalances across a membrane.
Methanogen
Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic conditions. They are classified as archaea, a group quite distinct from bacteria...
which is found in such diverse environments as oil wells, trash dumps, deep-sea hydrothermal vents, and oxygen-depleted sediments beneath kelp beds. Only M. acetivorans and microbes in the genus Methanosarcina
Methanosarcina
Methanosarcina are the only known anaerobic methanogens to produce methane using all three known metabolic pathways for methanogenesis. Most methanogens make methane from carbon dioxide and hydrogen gas. Some others utilize acetate in the acetoclastic pathway...
use all three known metabolic pathways for methanogenesis
Methanogenesis
Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with...
. http://www.genome.org/cgi/reprint/12/4/532.pdf Methanosarcinides, including M. acetivorans, are also the only archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
capable of forming multicellular colonies, and even show cellular differentiation. , the genome of M. acetivorans is the largest of all sequenced archaeal genomes.
In 2006, James G. Ferry and Christopher House discovered that M. acetivorans uses a previously unknown metabolic pathway
Metabolic pathway
In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function...
to metabolize carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
into methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
and acetate
Acetate
An acetate is a derivative of acetic acid. This term includes salts and esters, as well as the anion found in solution. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In...
using the well known enzymes phosphotransacetylase (PTS) and acetate kinase
Acetate kinase
In molecular biology, acetate kinase , which is predominantly found in micro-organisms, facilitates the production of acetyl-CoA by phosphorylating acetate in the presence of ATP and a divalent cation. The enzyme is important in the process of glycolysis, enzyme levels being increased in the...
(ACK). This pathway is surprisingly simple, and has been proposed by Ferry and House as perhaps the first metabolic pathway used by primordial microbes. Other theories of the primordial metabolic biochemistry include heterotrophic theory and chemoautotrophic theory, but both these theories have been criticised as being far too complex to have arisen spontaneously.
However, in the presence of minerals containing iron sulfides, as might have been found in sediments in a primordial environment, acetate would be catalytically converted into acetate thioester, a sulfur-containing derivative. Primitive microbes could obtain biochemical energy in the form of adenosine triphosphate
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
(ATP) by converting acetate thioester back into acetate using PTS and ACK, which would then be converted back into acetate thioester to complete the process. In such an environment, a primitive "protocell" could easily produce energy through this metabolic pathway, excreting acetate as waste. Furthermore, ACK catalyzes the synthesis of ATP directly. Other pathways generate energy from ATP only through complex multi-enzyme reactions involving protein pumps and osmotic imbalances across a membrane.
External links
- How Life Began: New Research Suggests Simple Approach Michael Schirber (LiveScience) 09 June 2006 09:09 am ET